Because a newly designed plane (with a rescue parachute, and a modern engine) is so much more expensive than one from the 1950s (leaded gas, possibly with grandfathered certification) everyone keeps flying the old ones. Cars have had many iterations on safety since the '55 Chevy, but planes not so many.
I think there can be little argument against the assertion that modernizing the general aviation fleet would improve safety. The majority of GA aircraft are using 60's technology carburetted reciprocating engines and running on leaded gasoline, and the cockpit is mostly analogue gauges with mechanical vacuum-driven gyros. Every car manufactured since the 90's uses fuel injection, yet GA pilots still need to worry about carburetor icing. That's not even going into other modern safety improvements like digital autopilot or ballistic recovery parachutes.
But for this comparison to make sense you need to assume that the counterfactual scenario involves zero decrease in air and car accidents between then and now.
This beggars belief; people seek to avoid accidents for other reasons than "regulators frown on them".
[1] https://en.wikipedia.org/wiki/Motor_vehicle_fatality_rate_in...
Edit: Interesting to note that pedestrian fatalities took a sharp rise from 2010
https://en.wikipedia.org/wiki/Motor_vehicle_fatality_rate_in...
More than that; the chart shows fatalities per vehicle mile starting at their all-time high and falling steadily thereafter. Exactly like you'd expect if people were trying to avoid fatalities. Nothing special happens in 1970, where fatalities per 100 million vehicle miles traveled have already fallen to 4.7 from, say, 21 in 1923.
47 years in the other direction, fatalities per 100 million vehicle miles traveled in 2017 are 1.16, a decline of 75.5% compared to the previous 47 years' 77.4%.
It might be that commercial interests often align with public safety and perception, but I bet that on the lower-end of the price spectrum, people would be willing to buy cars that endangered themselves and others. If only for lack of options.
Most people will say: "Yeah, it's a big unsafe (they won't even phrase it like that), but I will be more careful and it will be all right".
Then the next day they'll go to that party and drive home tipsy.
The cognitive dissonance won't even register.
This legislation is unlikely to change anytime soon.
Until a car is created that can take off from the streets and has low energy consumption, it cannot be said that we have a "flying car", at the moment we only have a "car-helicopter hybrid".